Connecting rod for sound reproducers



June 12, 1928. 1,673,574

D. R. LOVEJOY CONNECTING ROD FOR SOUND REPRODUCERS Filed Jan.

z 22 I INVENTOR fl/MM 77/2 10/00;

M55 2/ 4 i if ATTORNEYS Patented June 12, UNITED STATES PATENT OFFICE.

DIMMITT ROSS LOVEJOY, OF NEW YORK, N. Y., ASSIGNOR T LOVEJ'OY DEVELOPMENT CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

CONNECTING ROD FOR SOUND REPRODUCERS.

' Application filed January 21, 1926. I Serial No. 82,733.

Sound reproducers, of thetype in which the vibration of the armature of an electromagnet is utilized to bring about a corresponding vibration of a sound radiating member other than the armature itself, re-

quire some form of connection by which the movement of the armature is conferred upon the radiating member. A typical example of such apparatus is found in the so-called cone type loud speaker employed in radio receiving apparatus. Such apparatus illustrates in a marked degree the difficulty which the present invention is designed to obviate aid the invention will be described with par- 16 ticular reference to this type of sound reproducer, although the principles of the invention are applicable in general to all types in which a mechanical connection is to be employed between the armature of the electro magnet and the sound radiating member.

- Where the connecting member must serve to transmit a thrust in one direction and a pull in the opposite direction, the transmitting member must have a construction sufiiciently free from the tendency to bend to avoid substantial loss of power in transmitting the thrust. For this reason, in the cone type of loud speakers, the connecting rod is usually of such a stiffness that a very slight bend will develop a marked amount of tension or elastic force such that the rod itself would tend to vibrate transversely at its own natural frequency and introduce seriousdistortion due to this frequency being superposed'on the sound frequency which alone it is intended to transmit. As a matter of fact, in the constructidn of such loud speakers, it is so difficult to perfectly aline the sockets into which the twosends of the connecting rod are to be fitted, that the assembly of the complete unit commonly leaves the connecting rod in a state of elastic ten sion which is highly favorable to its assuming a vibration at its own natural frequency when excitation occurs. 1

The object of the present invention is to provide a form of connecting rod in which a slight disalinement of its two ends .may occur without setting up any substantial amount of elastic tension, while at the same time retaining the necessary quality of being able to transmit both thrust and tension forces. With such a construction, the assembly of the loud speaker unit with the two ends of the connecting rod in exact ,alinement, is no longer of such importance and the quality of reproduction is easier to maintain.

The invention is illustrated by way of example in the accompanying drawing, in which Figure 1 is a diametric section through the radiating member, illustrating the construction and location of the connecting rod between the radiating member and the vibrating armature of the electromagnet.

Figure 2 is a cross-section taken through the connecting rod on the line 2-2 of F ig ure 1. 4

Figure 3 is a central longitudinal section of a modified form of a. connecting rod constructed within the principles .and scope of the invention, and

Figure4 is a transverse section thereof on the line 44 of Figure 3.

Referring in detail to said drawing, and especially to Figure 1, l0 indicates'the radiating member, which may be any approved type of cone having the head 11 at its apex provided with a socket and set screw 12 to receive the outer end 13 of the connecting rod which has an intermediate portion 14, and whose inner end 15 is fixed as by soldering or otherwise in a perforation formed in the vibrating reed armature 16, rigidly secured at its base 17.- The armature 16 vibrates in front of the pole faces of the magnet core 18 'upon which are mounted the usual coils 19, 20 through which passes the. energizing current of fluctuating strength corresponding withthe sound to be reproduced. The present invention contemplates no change in the magnet itself and we may assume for example the ordinary form in which the core is permanently megnetized' and the total flux is altered by the actuating current in well known manner.

The construction of the connecting rod 13, 14;, 15, according to the present invention, comprises portions of reducedstiffness 21, 22, one near each end of the effective length, in conjunction with an intermediate stiff portion 14, the reduced portions 21, 22 being so short that while serving as universal 'joints they do not permit appreciable loss of power in transmitting thrust. The requirements are well satisfied, for example, by providing a relatively thin mandrel or core 23 of steel piano wire and reinforcing it at least throughout the intermediate portion 14 by a surrounding tube or sheath of a comparatively soft, light-weight material such as aluminum, of a thickness ample to insure sufficient stiffness to prevent bending between the points 21 and 22. The tube or may assume a simple cylindrical form such as illustrated in Figures 1 and 2, having sufficient cross-sectional area to insure adequate stiffness of the intermediate portion,

depending upon the physical properties of the material employed. On the other hand, the connecting rod may have a longitudinally flanged construction as illustrated, for

H example, in Figures 3 and 4, in which three symmetrically disposed flanges 14: are shown, without, however, intending to imply any particular limitation of the number 1 of tlise flanges, provided the effect is to give the required stiffness. It is equally apparent that the correct functioning of the device does not necessarily depend upon the continuity of the wire core through the intermediate portion, provided the ends of the reinforcing or stiffening sheath are adequately fixed or rigidly connected to the, wire 1 core. However, the continuous core is il lustrated, as it provides a satisfactory example of the invention, both as to its performance of the functions contemplated and with respect to simplicity of manufacture.

I have not thus far referred particularly to the construction of the end portions 13,,

15, for the reason that their design may differ widely according topreference, and

also because it depends to a considerable exi tent upon the precise form of the sound reproducing unit in which the connecting rod is to be employed. It is obvious, for exam f' that the portion of the connecting rod which extends. between the vibrating armature and the sound radiatin member constitutes the effective length of the rod,

in so far as its tendency to vibrate is concerned, and in principle there is no objection to providing the fiex1ble portions 21, 22

immediately adjacent the radiating member and the vibratory armature, in which event the longitudinal extent of the flexible portions 21, 22 might be so small as not to have any tendency to bend upon the application to'them of a longitudinally directed thrust. It is expedient, however, as a manufacturing consideration, to construct the'end portions, 13, 15 with sufficient length and stiflness to allow some choice of longitudinal adjustment of the composite connecting rod, in order to accommodate variations in the normal distance betweenthe vibratory armature and the radiating member. vThis distance will be unavoidably different in different units even of the same type. It is also a fact, as is well known, that occasional adjustment of the connection between the rod and the radiating member is necessary in use, for which reason the set screw 12 is provided. Inorder that these necessary adjustments in assembly and use of the reproducer may be provided for, the end portions 13, 15 are preferably made sufficiently stiff to avoid bending within their own lengths and thus confine the flexibility of the composite rod to the local points 21, 22, regardless of variations in adjustment. These terminal portions 13, 15 may be made stiff in much the same way as already described with refer ence to the intermediate portion 14, as, for example, by applying to them a cylindrical sheath of suitable metal which is securely fixed upon the wire core.

I claim 1. A connecting rod for sound reproducers comprising a relatively long intermediate portion of. suflicient stiffness to transmit thrust ,without substantial flexing, and a relatively flexible portion, near each end of its effectiye length, sufficiently short to trans mit thrust without substantial flexing, the unit thus'constituted admitting slight disalinement of its ends without developing substantial elastic strain:

2. A connecting rod for sound reproducers comprising an intermediate portion of relatively great stiffness, a short locally flexibleportion near each end of the effective length of the rod and terminal portions stifier than said flexible portions.

DIMMITT ROSS LOVEJOY. 

